Thanks for your reply. I can't imagine what it might have been, unless there was something in the hardscaping process that might have been a problem. I would love to get it analyzed, but, as you say, for what? And where? Who does that kind of analysis? It would probably be cheaper to get someone out to remove all of it and replace it with new, healthy soil.

Contact your local extenson service office or better full service nursery. They can direct you to soil testing labs in your area.

Removal and replacement is always an option but might be more of a project/ordeal than you think. To remove to a reasonable depth is bordering on a full cubic yard of soil. That's a lot of heavy material to remove and replace.........and may be unnecessary.

Yes; that would be a very last resort, and it would have to be hired out, which I would prefer to avoid. The extension service only tests for pH and recommends labs that will look at nutrient levels. I fertilize there, but not excessively so, so it can't be nutrients. I still wonder if it has something to do with the stonescape installation. Thanks for your reply!

My guess is it is highly compacted and acidic, or there is hard pan or an impervious object not far under the soil surface. Have you tried digging deep in the area? I was digging in such an area of my yard and found an old patio buried a couple inches under the soil (its an old property). Try digging it up and adding compost or organic material like shredded leaves or alfalfa pellets.

What Skip said - start digging way down. The possibilities are endless, especially if your area was settled long ago - oil tank, old wading pool (my neighbor found that), old patio, chunks of cement, old dry well (which means ballast stones, which will stop anything rooting). You may not need new soil, depending on what you find.

The simplest explanation is pH way out of whack, and usually that's from something like concrete. I'd get the pH tested first and go from there. Make sure you get a good representative sample - take it from several spots, a cylinder several inches deep, and mix them, then fill a clean jar or baggie.

Someone said 'acidic', I guess it could be, but there are not many ways for a patch like that to get permanently much more acidic than the surroundings, whereas concrete is a very common cause of high pH (alkaline). You didn't say where you are, East, West, arid, wet? What is the natural pH supposed to be there?

If it's not pH then take a sample to the soil lab and have it tested for nutrients - P and K (N is not that important yet so if it's extra $ you can skip it), Ca, Mg at a minimum. This test will also (should anyway) give an idea of total salts. If someone dumped a bag of softener salt there, the excess sodium can occupy all the exchange sites on the soil surface, displacing all the Mg, Ca, etc. and basically killing the soil for some time.

I would not start worrying about toxic contaminants till you eliminate the simplest and most commen causes. If there are no strange odors or colors, it's unlikely to be something like that. Even herbicides break down eventually. But it could be a persistent herbicide, or simply an amount large enough that it's lasting awhile. How long has it been bare?

It's pretty weird that you put 3" of bagged topsoil on top and grass still wouldn't grow. Whatever it is, it's fairly potent.